Samsung S2 (I9100) Lolipop Update
Back up important data on your Samsung Galaxy S2 as a full clean during flashing is required.
Settings> Developer Options> USB Debugging: USB debugging option on the enabling device.
Samsung Galaxy S2 must be rooted, unlocked and installed with a recovery tool TWRP or CWM like.
The device must be charged at least 60% power.Advertisement
- How to Update Galaxy S2 I9100 to Android 5.1 OmniROM:
Necessary files: OmniROM download Android 5.1 Lollipop custom firmware for Galaxy S2 i9100 from here and save it to your computer. Do not remove the content. Also download the Google Apps package for SGS2 from here.
Connect Galaxy S2 to your computer via USB and copy the zip file on the SD card phone cable.
Disconnect the USB cable and turn off the Galaxy S2.
Boot into recovery mode by pressing and holding the volume buttons up + Home + Power together.
Perform a Nandroid backup of your current operating system: Backup> Backup and Restore ClockworkMod recovery.
Clean data Task: from the CWM recovery menu, select restore wipe data / factory and confirm the process. Then go to delete cache partition and wipe the Dalvik cache.
From the recovery menu, select install zip from sdcard followed by choose zip from sdcard. Look for the OmniROM Android 5.1 custom firmware and confirm the flashing process.
Once this is done, repeat the previous step to install gapps on your smartphone.
After the installation is successful, return to the main recovery menu and restart the Samsung i9100 Galaxy S2 in the new custom ROM. The first boot takes about 5 minutes so please be patient.
How To Restore: To return to the previous operating system on your SGS2, boot into recovery, select the backup and restore then restore your previous ROM by selecting it from the list.